Inhomogeneous Mean-Field Approach to Collective Excitations Near the Superfluid-Mott Glass Transition
We develop an inhomogeneous quantum mean-field approach to the behavior of collective excitations across the superfluid–Mott glass quantum phase transition in two dimensions, complementing recent quantum Monte Carlo simulations (Puschmann et al. 2020). In quadratic (Gaussian) approximation, the Goldstone (phase) and Higgs (amplitude) modes completely decouple. Each is described by a disordered Bogoliubov Hamiltonian which can be solved by an inhomogeneous multi-mode Bogoliubov transformation. We find that the Higgs mode is spatially localized in both phases. The corresponding scalar spectral function shows a broad peak that is noncritical in the sense that its peak frequency does not soften but remains nonzero across the quantum phase transition. In contrast, the lowest-energy Goldstone mode delocalizes in the superfluid phase, leading to a zero-frequency spectral peak. We compare these findings to the results of the quantum Monte Carlo simulations. We also relate them to general results on the localization of bosonic excitations, and we discuss the limits and generality of our approach.
M. Puschmann et al., "Inhomogeneous Mean-Field Approach to Collective Excitations Near the Superfluid-Mott Glass Transition," Annals of Physics, vol. 435, no. Part 1, article no. 168526, Elsevier, Dec 2021.
The definitive version is available at https://doi.org/10.1016/j.aop.2021.168526
Center for High Performance Computing Research
Keywords and Phrases
Collective excitation; Disorder; Localization; Quantum phase transition; Superfluid
International Standard Serial Number (ISSN)
Article - Journal
© 2021 Elsevier, All rights reserved.
01 Dec 2021